The general aim of this project is to study placental metabolism and transfer function in chronic sheep preparations during maternal fasting and under conditions of reduced uterine blood flow. Placental utilization rates of oxygen, glucose, acetate and amino acids will be measured before and during fasting. The placenta transfer of antipyrine, ethanol and oxygen will be studied at different levels of maternal placental blood flow. The experimental results will be used to construct a theoretical model of placental transfer of inert molecules and oxygen.